Asymmetric half-bridge control method for driving motor of electric forklift

Abstract

The invention discloses an asymmetric half-bridge control method for a driving motor of an electric forklift, and the method comprises the steps: employing an asymmetric half-bridge as an inverter topology, and enabling the asymmetric half-bridge to comprise a left bridge arm and a right bridge arm; respectively constructing bridge arm models when the output ends of the left bridge arm and the right bridge arm are high levels, so as to obtain an expression of stator current of the driving motor; establishing a state equation taking the filter capacitor charge, the motor stator inductance magnetic flux and the filter inductance magnetic flux as state variables; and determining a stator current reference value according to the driving working condition of the forklift, setting a cost function, and selecting a switching control signal enabling the cost function to be minimum so as to control the switching action of the asymmetric half-bridge. According to the invention, the asymmetric half-bridge is used as the inverter topology to avoid the bridge arm direct connection problem, the state matrix of the electric drive system is obtained by carrying out overall modeling on the asymmetric half-bridge inverter, the torque ripple during the working of the motor can be effectively reduced, and the working stability of the motor is ensured.

Description

Technical Field

[0001] This invention belongs to the field of electric forklifts, and particularly relates to an asymmetric half-bridge control method for an electric forklift drive motor. Background Technology

[0002] Compared to ordinary electric vehicles, electric forklift drive motors have higher requirements for operational stability and DC voltage utilization. Traditional electric drive systems use full-bridge inverters to achieve AC-DC conversion. Full-bridge inverters have the problem of bridge arm shoot-through, which requires the addition of dead time to the drive signal. Dead time will reduce DC voltage utilization and introduce additional low-order harmonics, resulting in torque pulsation and affecting the smoothness of motor operation. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned problems in the prior art and provide an asymmetric half-bridge control method for electric forklift drive motors. By using an asymmetric half-bridge as the inverter topology, the shoot-through problem of the bridge arm is avoided. The state matrix of the electric drive system is obtained by modeling the asymmetric half-bridge inverter as a whole, and the drive motor is controlled by model predictive control. This can effectively reduce the torque ripple during motor operation and ensure the stability of motor operation.

[0004] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0005] A method for asymmetrical half-bridge control of an electric forklift drive motor includes:

[0006] An asymmetric half-bridge is used as the inverter topology, wherein the asymmetric half-bridge includes a left bridge arm and a right bridge arm;

[0007] Bridge arm models are constructed separately for the left and right bridge arms when their output terminals are at a high level, in order to obtain the expression for the stator current of the drive motor;

[0008] Establish a state equation with the filter capacitor charge, motor stator inductance flux, and filter inductance flux as state variables;

[0009] The stator current reference value is determined based on the forklift's operating conditions, and a cost function is set. The switching control signal that minimizes the cost function is selected to control the switching action of the asymmetrical half-bridge.

[0010] Furthermore, the left bridge arm is composed of a first switch and a second diode connected in series, and the right bridge arm is composed of a first diode and a second switch connected in series, to form an asymmetrical half-bridge;

[0011] The output terminals of the left and right bridge arms are respectively connected through a first filter inductor, a second filter inductor, a first filter capacitor, and a second filter capacitor, so that the first filter inductor and the second filter inductor, as well as the first filter capacitor and the second filter capacitor, form a parallel structure, and together with the stator inductor of the motor, they form an LCL-type filter.

[0012] Furthermore, the expression for the stator current of the drive motor is:

[0013]

[0014] Among them, i cf1 i represents the current of the first filter capacitor. cf2 P represents the current in the second filter capacitor. La1 P is the magnetic flux of the first filter inductor. La2 P is the magnetic flux of the second filter inductor. LM The magnetic flux of the stator inductance of the motor, u LM Where is the voltage across the motor stator inductor, LM is the inductance of the stator inductor, R is the equivalent load of the motor, and u La1 q is the voltage across the first filter inductor. cf sw represents the charge of the first and second filter capacitors, and sw is the control signal of the first switch.

[0015] Furthermore, the state equations established with the filter capacitor charge, motor stator inductance flux, and filter inductance flux as state variables include:

[0016] Let the state variables be:

[0017] x(t)=[q Cf p LM p La1 p La2 ] T

[0018] The derivative of the state variable is:

[0019]

[0020] The calculation yielded:

[0021]

[0022] Furthermore, the cost function is:

[0023]

[0024] The beneficial effects of this invention are:

[0025] 1. This invention avoids the bridge arm shoot-through problem by using an asymmetric half-bridge as the inverter topology. The state matrix of the electric drive system is obtained by modeling the asymmetric half-bridge inverter as a whole. The desired current of the inverter is determined according to the current forklift driving conditions. The difference between the desired current and the actual stator current is used as the cost function. The drive motor is controlled by model predictive control, which can effectively reduce the torque ripple of the motor during operation and ensure the stability of the motor operation.

[0026] 2. This invention avoids the shoot-through problem of bridge arms at the topology level, and avoids harmonics and torque ripple introduced by dead zones. By performing overall modeling of the asymmetric half-bridge inverter and motor to obtain the state matrix of the electric drive system, model predictive control is then performed, improving control accuracy. Attached Figure Description

[0027] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0028] Figure 1 This is a flowchart of the method of the present invention;

[0029] Figure 2 This is a schematic diagram of the asymmetric half-bridge inverter topology of the present invention;

[0030] Figure 3 This is a schematic diagram of the bridge arm model when point E is at a high level in this invention;

[0031] Figure 4 This is a schematic diagram of the bridge arm model when point F is at a high level in this invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] like Figure 1 The method for asymmetrical half-bridge control of an electric forklift drive motor, as shown, specifically includes the following steps:

[0034] Step 1: Use an asymmetric half-bridge as the inverter topology, wherein the asymmetric half-bridge includes a left bridge arm and a right bridge arm.

[0035] like Figure 2 As shown, U DC For DC voltage, C inThe input capacitor is P, and the DC side terminals are P and N, respectively. The left bridge arm consists of the first switch S1 and the second diode D2 connected in series, with the output terminal at point E. The right bridge arm consists of the first diode D1 and the second switch S2 connected in series, with the output terminal at point F, forming an asymmetrical half-bridge. It can be seen that the two bridge arms are asymmetrical, hence the name asymmetrical half-bridge. The output terminals of the left and right bridge arms are respectively connected to the first filter inductor L. a1 Second filter inductor L a2 First filter capacitor C f1 and the second filter capacitor C f2 So that the first filter inductor L a1 With the second filter inductor L a2 Between, the first filter capacitor C f1 With the second filter capacitor C f2 They all form a parallel structure and together with the stator inductance of the motor, they form an LCL-type filter.

[0036] Step 2: Construct bridge arm models for the left and right bridge arms when their output terminals are at a high level, respectively, to obtain the expression for the stator current of the drive motor.

[0037] like Figure 3 As shown, when point E is high, the model of the left bridge arm is as follows, where the red keys are connected to points P, N, and E, and (1) to (7) are the key numbers. e As the source of potential, S f For flow sources, 0 and 1 represent common potential nodes and common flow nodes, respectively.

[0038] like Figure 4 As shown, when point F is high, the model of the right bridge arm is as follows, where the red key is connected to points P, N, and E, and (1) to (7) are the key numbers. e As the source of potential, S f For flow sources, 0 and 1 represent common potential nodes and common flow nodes, respectively.

[0039] Based on the bridge arm model, the expression for the stator current of the drive motor is:

[0040]

[0041] Among them, i cf1 i represents the current of the first filter capacitor. cf2 P represents the current in the second filter capacitor. La1 P is the magnetic flux of the first filter inductor. La2 P is the magnetic flux of the second filter inductor. LM The magnetic flux of the stator inductance of the motor, u LM Where is the voltage across the motor stator inductor, LM is the inductance of the stator inductor, R is the equivalent load of the motor, and u La1q is the voltage across the first filter inductor. cf 1 represents the charge of the first filter capacitor and the second filter capacitor. sw represents the control signal of the first switch S1. Since the control signals of S1 and S2 are complementary, the control signal of the second switch S2 is 1-sw.

[0042] Step 3: Establish a filter capacitor charge q Cf Motor stator inductance flux p LM The state equation is a state equation where the filter inductor flux is the state variable, and the filter inductor flux includes the first filter inductor flux p. La1 Second filter inductor flux p La2 .

[0043] Let the system's state variables be:

[0044] x(t)=[q Cf p LM p La1 p La2 ] T (2)

[0045] The derivative of the state variable is:

[0046]

[0047] The following calculations were performed using the expression for the stator current of the drive motor:

[0048]

[0049] Step 4: Determine the stator current reference value based on the forklift's operating conditions, set the cost function, and select the switching control signal that minimizes the cost function to control the switching action of the asymmetrical half-bridge.

[0050] The cost function is:

[0051]

[0052] Where i * As a reference value for the stator current, sample u Cf i LM i La1 i La2 Calculate q Cf p LM p La1 p La2 u Cf For filter capacitor (C) f1 and C f2 The voltage across the terminals, i LM i is the current in the stator inductance (LM) of the motor. La1 The first filter inductor L a1The current, i La2 For the second filter inductor L a2 The current is calculated by predicting the state variables when sw is 0 and 1 respectively according to equation (4), and then calculating p. LM Substituting the predicted value into equation (5), and taking the sw corresponding to the minimum J, we can achieve model predictive control of the asymmetric half-bridge.

[0053] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0054] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for asymmetrical half-bridge control of an electric forklift drive motor, characterized in that, include: An asymmetric half-bridge is used as the inverter topology, wherein the asymmetric half-bridge includes a left bridge arm and a right bridge arm; Bridge arm models are constructed separately for the left and right bridge arms when their output terminals are at a high level, in order to obtain the expression for the stator current of the drive motor; Establish a state equation with the filter capacitor charge, motor stator inductance flux, and filter inductance flux as state variables; The stator current reference value is determined based on the forklift's operating conditions, and a cost function is set. The switching control signal that minimizes the cost function is selected to control the switching action of the asymmetrical half-bridge.

2. The asymmetric half-bridge control method for an electric forklift drive motor according to claim 1, characterized in that, The left bridge arm consists of a first switch and a second diode connected in series, and the right bridge arm consists of a first diode and a second switch connected in series, forming an asymmetrical half-bridge; The output terminals of the left and right bridge arms are connected to a first filter inductor, a second filter inductor, a first filter capacitor, and a second filter capacitor, respectively, so that the first filter inductor and the second filter inductor, as well as the first filter capacitor and the second filter capacitor, form a parallel structure, and together with the stator inductor of the motor, they form an LCL-type filter.

3. The asymmetric half-bridge control method for an electric forklift drive motor according to claim 1, characterized in that, The expression for the stator current of the drive motor is: Among them, i cf1 i represents the current of the first filter capacitor. cf2 P represents the current in the second filter capacitor. La1 P is the magnetic flux of the first filter inductor. La2 P is the magnetic flux of the second filter inductor. LM The magnetic flux of the stator inductance of the motor, u LM Where is the voltage across the motor stator inductor, LM is the inductance of the stator inductor, R is the equivalent load of the motor, and u La1 q is the voltage across the first filter inductor. cf sw represents the charge of the first and second filter capacitors, and sw is the control signal of the first switch.

4. The asymmetric half-bridge control method for an electric forklift drive motor according to claim 3, characterized in that, The state equations, with the filter capacitor charge, motor stator inductance flux, and filter inductance flux as state variables, include: Let the state variables be: x(t)=[q Cf p LM p La1 p La2 ] T The derivative of the state variable is: The calculation yielded:

5. The asymmetric half-bridge control method for an electric forklift drive motor according to claim 1, characterized in that, The cost function is:

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